I have little doubt that our enemies are capable of taking down sizable portions of our power grid. We know this, in part, because we’re capable of doing it to other countries and because we’ve detected Russian and Chinese hackers poking around inside our systems and planting malicious code. What’s less clear is how large a section of our grid could be taken down and for how long. Potentially, entire regions of the US could lose power for weeks or even longer. It’s worth noting, though, that we’ve been worried about such a catastrophic attack for decades